One of the essential functions of a system state estimator is to detect measurement errors, and to identify and eliminate them if possible. Measurements may contain errors due to various reasons. Large measurement errors can also occur when the meters have biases, drifts or wrong connections. Distribution networks are not measured with redundant number of meters, and thus this problem is very complex.
In most cases bad data detection can be done in state estimation preparation phase or after area estimation. However in order to be sure that all measurements are really correct, additional steps have to be taken.